Papers by Keyword: Homogeneous Precipitation

Abstract: The oxide phosphor (Y_1-xDy_x)₂O₃(x=0-0.1) was obtained by calcining their respective precursors synthesized by homogeneous precipitation technique using rare earth nitrate as mother salt and urea as precipitating agent. The particle shape/size, fluorescent properties (especially the influence of Dy³⁺ concentration and calcination temperature) of the product was studied in detail. The results showed that the precursors exhibit monodisperse spherical morphology whose size can be controlled by adjusting the urea content. The phase pure (Y_1-xDy_x)₂O₃ can be obtained by calcining precursor at least 600 °C, and the monodisperse spherical morphology can be kept at even high temperature of 1000 °C. The (Y_1-xDy_x)₂O₃ phosphors exhibit strong yellow emission at ~577 nm (⁴F_9/2→⁶H_13/2 transition of Dy³⁺) and blue emission at ~491 nm (⁴F_9/2→⁶H_15/2 transition of Dy³⁺) upon optimal excitation wavelength of ~352 nm. The quenching concentration of Dy³⁺ was determined to be ~2 at% (x=0.02). The emission intensity of (Y_1-xDy_x)₂O₃ phosphors can be improved with the temperature and particle size increasing

Abstract: A wide application of magnesium aluminate spinel powder has attracted a number of studies concerning the preparation of magnesium aluminate spinel powder. In this study, a precursor for magnesium aluminate spinel was synthesized by a homogeneous precipitation method using urea as a precipitant. The precursor and the calcined powders were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. After precipitation, the precursor was magnesium aluminium hydrate carbonate compound. By calcining, the precursor decomposed to MgO and an amorphous phase after calcining at 600°C. The formation of magnesium aluminate spinel via a reaction between MgO and the amorphous phase was observed after calcining over 800°C. The equiaxed magnesium aluminate spinel nanoparticles with particle size of 20-40 nm were obtained after calcining at 1100°C for 2 hours. Sinterability of the obtained magnesium aluminate spinel nanoparticles was also investigated by sintering compacts of magnesium aluminate spinel nanoparticles in the temperature interval of 1300-1650°C. Sintering temperature of 1600°C allowed the fabrication of dense magnesium aluminate spinel ceramics with relative density >95%.

Abstract: Ni-Fe layered double hydroxide containing carbonate anion (CO₃^2- ) has been successfully synthesized by a process of homogeneous precipitation involving urea hydrolysis under hydrothermal conditions. Factors that influence the composition and the crystallinity degree of NiFe-LDH, such as the molar fraction of urea/NO₃^- in solution, the total metal ion concentration in solution and the aging time, have been investigated in detail. Structure and morphology of the sample were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectra and scanning electron microscope (SEM). The results indicate NiFe-LDH with high purity present well-crystalline, uniform crystallite size

Abstract: Uniform spherical alumina powders have been synthesized via homogeneous precipitation method from aluminum nitrate using urea as the precipitant. The amount of ammonium sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical particles can be obtained when the molar ratio of ammonium sulfate to aluminum nitrate is about 0.72 and the concentration of the aluminum nitrate is 0.005M. Spherical alumina particles with 400 nm in diameter were obtained by calcining the precursors at 1100°C for 4 hrs.

Abstract: This paper mainly made a detailed review on cadmium-calcium hydroxyapatite solid solutions. There are including introduction, synthesis method and controlling conditions, and the summary of study results at home and abroad. Finally, gave the conclusion and prospect of the author.

Abstract: The homogeneous precipitation pathway was explored to synthesize ultrafine powders of Al(OH)₃. In the experiment, the scrap aluminum were used as raw material . The effects of reaction time, reaction temperature, stirring speed, concentration of sulphuric acid and dispersant on the preparation process were investigated. The results showed that ultrafine Al(OH)₃ powders can be yielded and well-controlled under the following optimal conditions: the concentration of sulphuric acid 3.0 mol•L^-1, reaction temperature 0-4 °C, stirring speed 900 r.min^-1 and reaction time 15 min. The diameter less than 100nm of sphericity Al(OH)₃ particles with the narrow distribution were successfully obtained. The Al(OH)₃ powders was analyzed with scanning electron microscopy , infrared spectrometer. The Al(OH)₃ powders have good dispersancy and purity is more than 90%. The operation of the experiment was very simple, and the particles were separated easily.

Abstract: Nanocrystalline ceria powder was prepared through homogeneous precipitation method, orthogonal experiment was designed to figure out the most important factor that influence the particle size of the resultant and the optimum condition. X-ray diffraction revealed that the as-prepared nanoscale ceria powder had cubic fluorite structure, TEM image showed that the ceria powder was weakly agglomerated with a particle size of about 10 nm.

Abstract: A facile and novel method was developed to fabricate highly porous CeO₂ surface on aluminum via a combination of homogeneous precipitation method and in situ growth process. After the introduction of CeO₂ film, aluminum exhibited excellent superhydrophobicity with contact angle of 152.9±1.5^o and a sliding angle of 5^o. SEM image of the film showed that the resulting surface exhibits a hierarchical micro- and nanostructure, which comprised of nanoleaves that grew perpendicular to the substrate and interleaved together to form a highly porous structure. This porous architecture, along with the low surface energy renders the aluminum superhydrophobicity.

Abstract: The water droplets in the microemulsion system of xylene/water/Span-80 can act as a micro-reactor which solubilize Zr(NO₃)₄, Y(NO₃)₃, and dimethyloxalate. The homogeneous precipitation reactions will take place in the restricted spaces determined by the droplets size. The micro-reactors help us obtain spherical nanometer ZrO₂(Y₂O₃) reunion powders successfully. The spherical nanometer ZrO₂(Y₂O₃) reunion powders and the precursor powders were characterized by means of TG-DTA, XRD, SEM and laser particle analyzer. It was investigated that the effect of Span-80 concentration on morphology and crystal phase composition of reunion powders. The result shows that as the volume ratio V_xylene:VSpan_-80:V_water= 40:1.0:8, the well spherical and excellent dispersion reunion powders with size of 4-16um were prepared after the precursor powders were sintered at 600°C for 2h. The Span-80 concentration has no effect on the crystal phase composition of reunion powders, however, has significant effect on the morphology of reunion powders.

Abstract: Metal ions doped complex cobalt blue pigments are prepared by homogeneous precipitation, to investigate the effects of doping ions Zn²⁺ ，Mg²⁺ ，Ni²⁺ and Y ³⁺ on some properties of the doped complex cobalt blue pigments, such as crystal structure, color, shading power and temperature resistance. Studies have shown that doping have little effect on the spinel crystal type and temperature resistance of the pigments ; ionic radius differences between doping ions and Co^{2 +} cause lattice distortion and changes of lattice constant , thus affecting the ligand state spaces of Co^{2 +} ion, color and shading power of complex cobalt blue pigment. The lattice constant of Zn^{2 +} doped complex cobalt blue becomes larger with the increasing amount of Zn^{2 +} ; while doping Mg^{2 +}and Ni^{2 +} , the crystal lattice constants become smaller; when doping with Y^{3 +} , Y^{3 +} ions enter into CoAl₂O₄ lattice, replacing some hexa-coordinate octahedral gap of Al^{3 +} , ionic radius differences between Y^{3 +} and Al³⁺cause lattice distortion, when doping amount of Y ^{3 +} increases to a certain extent, the phase in the form of Y₂O₃ will be generated and it will maybe form a kind of CoY_xAl_2-xO₄- Y₂O₃ solid solution instead of the complete spinel structure.